Method and system for recovering and purifying a gaseous sterilizing agent

ABSTRACT

A system and method for recovering a sterilization agent from waste gaseous mixture, comprising a gas separator to wash waste gas comprising a gaseous mixture of a sterilization agent, insert dilution gases, and water vapor, from plurality sterilization chambers, with water, thereby producing a water-gaseous sterilization agent mixture collected at bottom section of the gas separator, and inert dilution gases exhausted at top section of the gas separator; a pressure reducing valve; a first tank or gas evaporator to produce gaseous sterilization agent and water vapor; a first condenser to produce condensed water vapor and separate the gaseous sterilization agent from the condensed water vapor; a water tank to receive the condensed water vapor; a separation pump for raising pressure of the gaseous sterilization agent; a second condenser to cool the gaseous sterilization agent causing the sterilization agent to condense into liquid; and a second tank for storing the liquid sterilization agent.

FIELD OF THE DISCLOSURE

The present disclosure relates to gaseous sterilization agents, and more specifically to a method and system for recovering and purifying a gaseous sterilization agent.

BACKGROUND

Ethylene oxide (ETO) is a highly reactive organic compound whose high reactivity makes it useful in many different applications. Due to the high reactivity of ETO, ETO may be used as a surface disinfectant, or sterilizing agent. ETO as a sterilizing agent is well known for its effectiveness to sterilize objects at certain gas concentrations. The objects for sterilization are placed in a hermitically sealed chamber. ETO vapor is then pumped into the chamber to sterilize the objects.

However, due to the high reactivity, ETO gas is extremely flammable, toxic, and explosive. Even in the absence of air, ETO must be used with extreme caution in high concentrations at low pressures for sterilization purposes. Presently, high concentration ETO gas is not recyclable and may be used only once. After use, the ETO gas is then discharged to an emission control device for destruction.

There are a few current approaches for addressing the problem of emission and disposal of the ETO toxic gas, which solves one problem in exchange for creating another problem. For example, if ETO is absorbed into water, then the problem then becomes the treatment and discharge of the toxic water. If one tries to dispose of ETO by combustion means, the problem then becomes how to prevent an explosion (e.g., prevent an explosive reaction).

One method for reusing ETO gas involves the use of a low concentration mixture of ETO and an inert gas at higher process pressures. High process pressures (e.g., up to 4 atmospheres) allow an increase in the ETO gas concentration to an acceptable milligram per liter value for effective sterilization. Mixtures having ratios of ETO to inert gas of 10/90 and 20/80 are generally used. These mixtures have sufficient ETO concentrations to sterilize objects regardless of the material being sterilized under normal temperature and at above atmospheric pressure conditions. Relative non-flammability of diluted ETO and inert gas mixtures allows for the recycling of these mixtures. However, these mixtures are not as effective as higher concentrations of ETO gas for sterilization.

In addition, the concentration of ETO decreases with continual use during the sterilization process since ETO is consumed in reacting with bacteria, water vapor, alcohol and the like during the sterilization process. Furthermore, the ETO gas concentration may be reduced to an unsatisfactory concentration level to provide a consistent sterilization effect. Thus, low concentration gas mixtures require processing using higher pressure rated vessels, which are more expensive. This process further involves processing the gases at above atmospheric pressures which carries the risk of fugitive and catastrophic leakage. Consequently, in the industry today, all large ETO sterilizer chambers are designed to operate using low pressure and high concentrations of ETO gas. Existing sterilizers in use in the industry are not rated for the higher pressures that are required to recycle the low concentration ETO gas sterilant.

Thus, it is desirable to provide a system and method for recycling sterilant gas mixtures to a high concentration of ETO gas to obtain maximum sterilization effectiveness while minimizing the complexity of the process and the cost of the sterilization equipment. It is desirable to provide a system that can be retrofitted to existing sterilization facilities, by the utilization of the existing sterilization process equipment and avoiding the expenses that are associated with complete system replacement.

Furthermore, when several large sterilization chambers are coupled together at the exhaust, as often the case in large commercial sterilization facilities, it is possible for the multiple chambers to exhaust waste gas stream simultaneously. This causes the peak flow rate of the resulting total waste gas stream to become multiple times greater than the flow rate if the waste gas stream is exhausted from a single sterilization chamber. Therefore, in order to process the greater flow of waste gas stream for recycling sterilant gas to a high concentration, a correspondingly larger sized system is required.

A larger sized apparatus would mean increased size of the condensers, separation pump, piping, valves as well as the cooling systems that cools the condensers. Hence, the initial capital cost would be significantly increased to procure and install such large sized apparatus, as would the costs for handling and operating such a large sized apparatus, specifically with respect to high cooling costs. In addition, space required for the installation would also be increased, which might be problematic for existing facilities where available space is already limited.

Therefore, it is desirable to limit the size increase of the recycling apparatus when handling excessively large waste gas stream flow, and to limit the cooling energy consumption of the recycling apparatus when handling excessively large waste gas stream flow.

SUMMARY

There is thus provided, in accordance with some embodiments of the present disclosure, a system for recovering a sterilization agent from a waste gaseous mixture may include a pressure reducing valve for reducing a pressure of a waste gas from one or more sterilization chambers to a first predefined pressure. The waste gas may include a gaseous mixture of a sterilization agent, nitrogen gas, and water vapor. A first condenser may be configured to receive the gaseous mixture via the pressure reducing valve, and to cool the gaseous mixture to a temperature below a boiling point temperature and above a freezing point temperature of the water vapor at the first predefined pressure. A first tank, coupled to the first condenser, may store the condensed water vapor separated from the gaseous mixture in the first condenser. A separation pump coupled to the first tank may raise the pressure of the gaseous mixture to a second predefined pressure. A second condenser may be configured to receive the gaseous mixture from the separation pump, to cool the gaseous mixture to a temperature below a boiling point temperature and above a freezing point temperature of the sterilization agent at the second predefined pressure causing the sterilization agent to condense into a liquid, and to discharge the nitrogen gas remaining in the gaseous mixture. A second tank, coupled to the second condenser, may store the sterilization agent separated from the gaseous mixture in the second condenser.

Furthermore, in accordance with some embodiments of the present disclosure, the sterilization agent may include ethylene oxide (ETO).

Furthermore, in accordance with some embodiments of the present disclosure, the first predefined pressure may be 1 pound per square inch and the second predefined pressure is atmospheric pressure.

Furthermore, in accordance with some embodiments of the present disclosure, the boiling point temperature of the water vapor may be 20 deg C. when the pressure of the gaseous mixture is 1 psi.

Furthermore, in accordance with some embodiments of the present disclosure, boiling point temperature of the ETO may be 10 deg C. when the pressure of the gaseous mixture is atmospheric pressure.

Furthermore, in accordance with some embodiments of the present disclosure the sterilization agent may be propylene oxide.

Furthermore, in accordance with some embodiments of the present disclosure, the system may include a chamber evacuation pump coupled to the pressure reducing valve for pumping the waste gas into the first condenser.

Furthermore, in accordance with some embodiments of the present disclosure, the system may include an exhaust warmer and a freezer economizer for recovering cooling energy in the system.

Furthermore, in accordance with some embodiments of the present disclosure, the system may include one or more H₂O freezers coupled to the first condenser and the separation pump, and wherein each of the one or more H₂O freezers may freeze H₂O molecules in the water vapor to a freezer surface.

Furthermore, in accordance with some embodiments of the present disclosure, at least two H₂O freezers from the one or more H₂O freezers may be connected in parallel coupled between the first condenser and the separation pump.

Furthermore, in accordance with some embodiments of the present disclosure, the system may include an ETO freezer coupled to the second condenser for trapping residual vapors of the sterilization agent.

Furthermore, in accordance with some embodiments of the present disclosure the system may include a waste gas holding tank coupled to the pressure reducing valve and to the one or more sterilization chambers for collecting the waste gas from the one or more sterilization chambers.

Furthermore, in accordance with some embodiments of the present disclosure, the system may include one or more ETO pre-condensers placed in series before the second condenser, wherein each of the one or more pre-condensers may have progressively lower temperatures above the temperature of the second condenser.

There is further provided, in accordance with some embodiments of the present disclosure, a method for recovering a sterilization agent from a waste gaseous mixture that may include receiving a waste gas from a sterilization chamber. The waste gas may include a gaseous mixture of a sterilization agent, nitrogen gas, and water vapor, A pressure of the gaseous mixture may be reduced to a first predefined pressure so as to reduce a boiling point temperature of the sterilization agent to below the freezing point temperature of the water vapor in the gaseous mixture. The gaseous mixture with the pressure at the first predefined pressure may be cooled to a temperature below a boiling point temperature and above the freezing point temperature of the water vapor. Condensed water vapor may be removed from the gaseous mixture. The pressure of the gaseous mixture may be raised to a second predefined pressure greater than the first predefined pressure so as to elevate a boiling point temperature of the sterilization agent in the gaseous mixture. The gaseous mixture at the second predefined pressure may be cooled to a temperature below the boiling point temperature and above a freezing point temperature of the sterilization agent causing the sterilization agent to condense into a liquid. The liquid sterilization agent may be separated from the gaseous mixture so as to recover the sterilization agent for reuse from the waste gas. The nitrogen gas remaining in the gaseous mixture may be discharged.

Furthermore, in accordance with some embodiments of the present disclosure, the sterilization agent may include ethylene oxide (ETO).

Furthermore, in accordance with some embodiments of the present disclosure, the first predefined pressure may be 1 pound per square inch (psi) and the second predefined pressure may be atmospheric pressure.

Furthermore, in accordance with some embodiments of the present disclosure, the boiling point temperature of the water vapor may be 20 deg C. when the pressure of the gaseous mixture is 1 psi.

Furthermore, in accordance with some embodiments of the present disclosure, the boiling point temperature of the ETO may be 10 deg C. when the pressure of the gaseous mixture is atmospheric pressure.

Furthermore, in accordance with some embodiments of the present disclosure, the sterilization agent may be propylene oxide.

Furthermore, in accordance with some embodiments of the present disclosure, discharging the nitrogen gas may include discharging the nitrogen gas to the atmosphere or collecting the discharged nitrogen as for reuse.

Furthermore, in accordance with some embodiments of the present disclosure, the method may include recovering cooling energy in the system by using; an exhaust warmer and a freezer economizer.

Furthermore, in accordance with some embodiments of the present disclosure, the method may include freezing H₂O molecules in the water vapor to a freezer surface of one or more H₂O freezers.

Furthermore, in accordance with some embodiments of the present disclosure, at least two H₂O freezers from the one or more H₂O freezers may be connected in parallel, and the method may include defrosting at least one of the H₂O freezers from the at least two parallel H₂O freezers.

Furthermore, in accordance with some embodiments of the present disclosure, the method may include trapping residual vapors of the sterilization agent using, one or more ETO freezers coupled to the second condenser

Furthermore, in accordance with some embodiments of the present disclosure, at least two ETO freezers from the one or more FLO freezers may be connected in parallel, and the method may include defrosting at least one of the ETO freezers from the at least two parallel ETO freezers.

Furthermore, in accordance with some embodiments of the present disclosure, the method may include collecting the waste gas from the one or more sterilization chambers in a waste gas holding tank.

Furthermore, in accordance with some embodiments of the present disclosure, the method ma include setting the temperatures of each of one or more ETO pre-condensers placed in series before the second condenser to progressively lower temperatures above the temperature of the second condenser.

There is further provided, in accordance with the present disclosure, a system for recovering a sterilization agent from a waste gaseous mixture, the system may include a gas separator configured to wash waste gas from one or more sterilization chambers, with water, the waste gas comprising a gaseous mixture of a sterilization agent, inert dilution gases, and water vapor, thereby the gaseous sterilization agent and water vapor are absorbed by the water creating a water-gaseous sterilization agent mixture that is collected at a bottom section of the gas separator, and the inert dilution gases are exhausted at a top section of the gas separator; a pressure reducing valve for reducing a pressure of the water-gaseous sterilization agent mixture to a first predefined pressure; a first tank or a gas evaporator, coupled to the pressure reducing valve, configured to receive the water-gaseous sterilization agent mixture, and to heat the water-gaseous sterilization agent mixture to a temperature above boiling point temperature of the sterilization agent and above a freezing point temperature of the water to produce gaseous sterilization agent and water vapor; a first condenser configured to receive gaseous sterilization agent and water vapor via the first tank or the gas evaporator, and to cool the gaseous sterilization agent and water vapor to a temperature below a boiling point temperature and above a freezing point temperature of the water vapor at the first predefined pressure to produce condensed water vapor and to separate the gaseous sterilization agent from the condensed water vapor; a water tank, coupled to the first condenser, configured to receive the condensed water vapor, wherein when the first tank heats the water-gaseous sterilization agent mixture, the water tank is the same tank as the first tank, and when the gas evaporator heats the water-gaseous sterilization agent mixture, the water tank is in addition to the first tank; a separation pump coupled to the first condenser for raising the pressure of the gaseous sterilization agent to a second predefined pressure;

a second condenser, configured to receive the gaseous sterilization agent from the separation pump, to cool the gaseous sterilization agent to a temperature below a boiling point temperature and above a freezing point temperature of the sterilization agent at the second predefined pressure causing the sterilization agent to condense into a liquid; and a second tank, coupled to the second condenser, for storing the liquid sterilization agent.

Furthermore, in accordance with some embodiments of the present disclosure, the sterilization agent may comprise ethylene oxide (ETO).

Furthermore, in accordance with some embodiments of the present disclosure, the first predefined pressure may be 1 pound per square inch and the second predefined pressure may be atmospheric pressure.

Furthermore, in accordance with some embodiments of the present disclosure the boiling point temperature of the water vapor may be 20 deg C. when the pressure of the gaseous mixture is 1 psi.

Furthermore, in accordance with some embodiments of the present disclosure, the boiling point temperature of the ETO may be 10 deg C. when the pressure of the gaseous mixture is atmospheric pressure.

Furthermore, in accordance with some embodiments of the present disclosure, the sterilization agent may be propylene oxide.

Furthermore, in accordance with some embodiments of the present disclosure, the system may further comprise a chamber evacuation pump coupled to the gas separator for pumping the waste gas into the gas separator.

Furthermore, in accordance with some embodiments of the present disclosure, the system may further comprise an exhaust warmer and a freezer economizer for recovering cooling energy in the system.

Furthermore, in accordance with some embodiments of the present disclosure, the system may further comprise one or more H₂O freezers coupled to the first condenser and the separation pump, and wherein each of the one or more H₂O freezers freezes H₂O molecules in the water vapor to a freezer surface.

Furthermore, in accordance with some embodiments of the present disclosure, at least two H₂O freezers from the one or more H₂O freezers may be connected in parallel, coupled between the first condenser and the separation pump.

Furthermore, in accordance with some embodiments of the present disclosure, the system may further comprise one, or more ETO freezers coupled to the second condenser for trapping residual vapors of the sterilization agent.

Furthermore, in accordance with some embodiments of the present disclosure, at least two ETO freezers from the one or more ETO freezers may be connected in parallel.

Furthermore, in accordance with some embodiments of the present disclosure, the system may further comprise one or more ETO pre-condensers placed in series before the second condenser, wherein each of the one or more pre-condensers may have progressively lower temperatures above the temperature of the second condenser.

There is further provided, in accordance with the present disclosure, a method for recovering a sterilization agent from a waste gaseous mixture, the method may include receiving a waste gas from one or more sterilization chambers, the waste gas comprising a gaseous mixture of a sterilization agent, inert dilution gases, and water vapor; washing the gaseous mixture with water by a gas separator, thereby absorbing the sterilization agent and water vapor in the water, creating a water-gaseous sterilization agent mixture; collecting the water-gaseous sterilization agent mixture at a bottom section of the gas separator, and exhausting the inert dilution gases at a top section of the gas separator; reducing a pressure of the water-gaseous sterilization agent mixture to a first predefined pressure so as to reduce a boiling point temperature of the sterilization agent to below a freezing point temperature of water in the water-gaseous sterilization agent mixture; heating the water-gaseous sterilization agent mixture to a temperature above boiling point temperature of the sterilization agent and above a freezing point temperature of the water to produce gaseous sterilization agent and water vapor; cooling the gaseous sterilization agent and water vapor with the pressure at the first predefined pressure by a first condenser, to a temperature below a boiling point temperature and above the freezing point temperature of the water vapor, and removing condensed water vapor from the gaseous sterilization agent; raising the pressure of the gaseous sterilization agent by a separation pump, to a second predefined pressure greater than the first predefined pressure so as to elevate a boiling point temperature of the sterilization agent, said separation pump being coupled to the first condenser, or the upper portion of the first tank; cooling, the gaseous mixture at the second predefined pressure, by a second condenser, to a temperature below the bailing point temperature and above a freezing point temperature of the sterilization agent causing the sterilization agent to condense into a liquid, thereby collecting the liquid sterilization agent for reuse.

Furthermore, in accordance with some embodiments of the present disclosure, the sterilization agent may comprise ethylene oxide (ETO).

Furthermore, in accordance with some embodiments of the present disclosure, the first predefined pressure may be 1 pound per square inch (psi) and the second predefined pressure may be atmospheric pressure.

Furthermore, in accordance with some embodiments of the present disclosure, the boiling point temperature of the water vapor may be 20 deg C. when the pressure of the gaseous mixture is 1 psi.

Furthermore, in accordance with some embodiments of the present disclosure, the boiling point temperature of the ETO may be 10 deg C. when the pressure of the gaseous mixture is atmospheric pressure.

Furthermore, in accordance with some embodiments of the present disclosure, the sterilization agent may be propylene oxide.

Furthermore, in accordance with some embodiments of the present disclosure, the exhausting inert dilution gases may comprise discharging nitrogen gas or CO₂ gas or a combination thereof, to the atmosphere or collecting the exhausted inert dilution gases comprising nitrogen gas or CO₂ gas or a combination thereof, for reuse.

Furthermore, in accordance with some embodiments of the present disclosure, the method may further comprise recovering cooling energy in the system by using an exhaust warmer and a freezer economizer.

Furthermore, in accordance with some embodiments of the present disclosure, the method may further comprise freezing H₂O molecules in the water vapor to a freezer surface of one or more H₂O freezers.

Furthermore, in accordance with some embodiments of the present disclosure, at least two H₂O freezers from the one or more H₂O freezers may be connected in parallel, and further comprising defrosting at least one of the freezers from the at least two parallel H₂O freezers.

Furthermore, in accordance with some embodiments of the present disclosure, the method may further comprise trapping residual vapors of the sterilization agent using one or more ETO freezers coupled to the second condenser.

Furthermore, in accordance with some embodiments of the present disclosure, at least two ETO freezers from the one or more H₂O freezers may be connected in parallel, and further comprising defrosting at least one of the ETO freezers from the at least two parallel ETO freezers.

Furthermore, in accordance with some embodiments of the present disclosure, the method may further comprise setting the temperatures of each of one or more ETO pre-condensers placed in series before the second condenser to progressively lower temperatures above the temperature of the second condenser.

BRIEF DESCRIPTION OF THE DRAWINGS

In order for the embodiments of the present disclosure to be better understood and for its practical applications to be appreciated, the following Figures are provided and referenced hereafter. It should be noted that the Figures are given as examples only and in no way limit the scope of the embodiments of the present disclosure. Like components are denoted by like reference numerals.

FIG. 1 schematically illustrates a block diagram of a first embodiment of a system for recovering a sterilization agent from a waste gaseous mixture, in accordance with some embodiments of the present disclosure;

FIG. 2 schematically illustrates a block diagram of a second embodiment of a system for recovering a sterilization agent from a waste gaseous mixture, in accordance with some embodiments of the present disclosure;

FIG. 3 schematically illustrates a block diagram of a third embodiment of a system for recovering a sterilization agent from a waste gaseous mixture, in accordance with some embodiments of the present disclosure;

FIG. 4 schematically illustrates a block diagram of a fourth embodiment of a system for recovering a sterilization agent from a waste gaseous mixture, in accordance with some embodiments of the present disclosure;

FIG. 5 schematically illustrates a block diagram of a fifth embodiment of a system for recovering a sterilization agent from a waste gaseous mixture, in accordance with some embodiments of the present disclosure;

FIG. 6 schematically illustrates a block diagram of a sixth embodiment of a system for recovering a sterilization agent from a waste gaseous mixture, in accordance with some embodiments of the present disclosure;

FIG. 7 is a flowchart depicting a method for recovering a sterilization agent from a waste gaseous mixture, in accordance with some embodiments of the present disclosure;

FIG. 8 schematically illustrates a block diagram of an embodiment of a system for recovering a sterilization agent from a waste gaseous mixture from one or more sterilization chambers, in accordance with some embodiments of the present disclosure;

FIG. 9 schematically illustrates a block diagram of an embodiment of a system for recovering a sterilization agent from a waste gaseous mixture from one or more sterilization chambers, in accordance with some embodiments of the present disclosure; and

FIG. 10 is a flowchart depicting a method for recovering a sterilization agent from a waste gaseous mixture from one or more sterilization chambers, in accordance with some embodiments of the present disclosure.

DETAILED DESCRIPTION

In the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of the embodiments of the disclosure. However, it will be understood by those of ordinary skill in the art that the embodiments of the disclosure may be practiced without these specific details. In other instances well-known methods, procedures, components, modules, units and/or circuits hake not been described in detail so as not to obscure the embodiments of the disclosure.

Although embodiments of the disclosure are not limited in this regard, discussions utilizing terms such as, for example, “processing,” “computing,” “calculating,” “determining,” “establishing”, “analyzing”, “checking”, or the like, may refer to operation(s) and/or process(es) of a computer, a computing platform, a computing system, or other electronic computing device, that manipulates and/or transforms data represented as physical (e.g., electronic) quantities within the computer's registers and/or memories into other data similarly represented as physical quantities within the computer's registers and/or memories OT other information non-transitory storage medium (e.g., a memory) that may store instructions to perform operations and/or processes. Although embodiments of the disclosure are not limited in this regard, the terms “plurality” and “a plurality” as used herein may include, for example, “multiple” or “two or more”. The terms “plurality” or “a plurality” may be used throughout the specification to describe two or more components, devices, elements, units, parameters, or the like. Unless explicitly stated, the method embodiments described herein are not constrained to a particular order or sequence. Additionally, some of the described method embodiments or elements thereof can occur or be performed simultaneously, at the same point in time, or concurrently. Unless otherwise indicated, use of the conjunction “or” as used herein is to be understood as inclusive (any or all of the stated options).

Embodiments of the present disclosure herein describe a method and a system for recovering a sterilization agent from a waste gaseous mixture. The sterilization agent as described herein may be, for example, ethylene oxide (ETO). The system may operate at pressure below and/or at atmospheric pressure and use few moving parts. The energy efficient system may be configured to recover ETO that is clean and reusable while emitting an exhaust with a level of Fro at part-per-million (ppm) levels.

After the sterilization agent is used for sterilizing items and/or objects on a closed sealed sterilization chamber, the sterilization waste gas pumped out of the sterilization chamber may include a gaseous mixture of inert nitrogen gas, the sterilization agent, such as ethylene oxide gas, and water vapor. This system leverages the differences in the vapor pressures, and the boiling and freezing points of these three gases in order to separate them. As a result, clean nitrogen gas and liquid water may be safely isolated and disposed of, while the valuable ethylene oxide gas may be recollected at high purity, suitable to be reused after appropriate quality testing.

In the embodiments taught herein, the process for recovering a sterilization agent from a waste gaseous mixture may be achieved by lowering the gas pressure to a level where the freezing point of the two components are drastically different. The ethylene oxide molecules have sufficient energy to remain in the gas phase but does not covalently bind to water molecules that are being condensed and cooled from liquid phase, and removing the water from the mixture. In some embodiments, the mixture may be further cooled such that the water molecules may be frozen into the solid phase and the solid removed.

The pressure of the dry ethylene oxide gas may be then raised to normal atmospheric pressure so as to elevate its boiling point so as to condense the ETO into a liquid, which may be removed from the nitrogen gas component of the mixture. At the end of the process, pure, uncontaminated ethylene oxide liquid may be collected, ready to be inspected and reused. Clean waste water, safe and free from ethylene oxide contamination may be collected, tested and then discharged into the environment, for example. Similarly, the separated nitrogen gas, used in the sterilization process, may be discharged into an abatement system or into the atmosphere.

This is a “clean” process where the only waste products are nitrogen gas and water. No absorption materials or metal catalysts are needed, which would need to be disposed of periodically. This is also an intrinsically safe process the operation in that the waste gas from the sterilization chamber is maintained at or below atmospheric pressure, so that there is no ethylene oxide gas leakage out from the system. Furthermore, this ‘cold’ process may be carried out at near normal sterilization temperatures to cryogenic temperatures minimizing the risk of catastrophic explosions by staying well below ethylene oxide's autoignition temperature.

In the context of the present disclosure, two elements that are coupled to in the systems shown herein may refer to elements that may be physically connected together by tubes and pipes, for example, that may be thermally isolated to carry refrigerants, hermetic seals for preventing leaks, pressure valves, flanges, connectors and the like. The terms used herein such as waste gas, gaseous mixture, waste gaseous mixture, gas streams are all synonymous. They refer to a waste gas that is a gaseous mixture of chemical components emitted from a sterilization chamber that is progressively processed to remove, separate and/or purify the sterilization agent from the waste gas. These terms may refer to the original waste gas with all of its chemical components exiting the sterilization chamber, or the waste gas with any or part of its chemical components removed at any step of the process in recovering the sterilization agent.

FIG. 1 schematically illustrates a block diagram of a first embodiment of a system 10 for recovering a sterilization agent from a waste gaseous mixture, in accordance with some embodiments of the present disclosure. System 10 may include a sterilization chamber 1 coupled to a H₂O condenser 30 (also known herein as a first condenser) and an ETO condenser 50 (also known herein as a second condenser). H₂O condenser 30 may be coupled to H₂O tank 300 (also known herein as a first tank), and Fro condenser 50 may be coupled to ETO tank 500 (also known herein as a second tank). H₂O tank 300 and ETO tank 500 may be respectively used for storing the H₂O liquid and ETO during their separation processes from the gaseous mixture. The gaseous mixture of waste gas from sterilization chamber 1 may be pumped into H₂O condenser 30 via a pressure reducing valve 3 using a chamber evacuation pump 2.

In some embodiments of the present disclosure, pressure reducing valve may reduce the pressure of the gaseous mixture pumped into H₂O condenser 30 to a first predefined value such as 1 psi (e.g., pound per square inch), for example, or any suitable pressure value, so as to reduce the boiling point temperature of the sterilization agent vapor component in the waste gas. The system elements operating at a reduced pressure are shown in reduced pressure region 35 (e.g., inside the dotted rectangle).

In some embodiments of the present disclosure, sterilization chamber 1 may include an enclosure with the objects and/or items to be sterilized, configured to withstand pressure variances. Sterilization chamber 1 may include inlet and/or outlet ports for removing air, injecting sterilization agent gases, and removing waste gases.

In some embodiments of the present disclosure, chamber evacuation pump 2 may include vacuum pumps of various types, capable of removing the waste gas from sterilization chamber 1.

In some embodiments of the present disclosure, system 10 may include pressure reduction valve 3 which may be a throttling valve, capable of reducing and maintaining system pressure in reduced pressure region 35.

In some embodiments of the present disclosure, H₂O condenser 30 may include a shell-tube, plate or other type of heat exchanger, which may be cooled by chilled water or refrigerants. H₂O condenser 30 may condense and trap water vaper and other contaminants, such as oil used by chamber evacuation pump 2. H₂O condenser 30 may also allow clean ETO gas, together with other inert gases, such as nitrogen (N₂), to pass into ETO condenser 50.

For a pressure of 1 psi, the boding point of water may be reduced to 20 deg C., while the boiling point of ETO is 45 deg C. H₂O condenser 30 may be a heat exchanger that chills the gas mixture to about 4 deg C. to condense the water vapor and contaminants from the sterilization process of the items and/or objects in sterilization chamber 1 such as oil, polymers formed by the sterilization agent, for example, that may be mixed into the water vapor.

An H₂O discharge valve 301 may be used to discharge H₂O and other contaminants stored in H₂O tank 300. Similarly, a vacuum release valve 302 may be used to release the vacuum inside reduced pressure region 35 so as to facilitate the discharge of material such as N₂ from H₂O tank 300.

In some embodiments of the present disclosure, the gaseous mixture with the water vapor removed in reduced pressure region 35 may be pumped into ETO condenser 50 by a separation pump 4 via a separation valve 4A, which separates reduced pressure region 35 in system 10 from normal pressure region 36 in system 10. Separation valve 4A may allow the gaseous mixture with the water vapor removed to enter separation pump 4 which pumps the gaseous mixture into ETO condenser 50 while raising the pressure of the gaseous mixture to near atmospheric pressure.

In some embodiments of the present disclosure, separation pump 4 may include a vacuum pump capable of maintaining reduced pressures in reduced pressure region V (e.g., the region shown from pressure reduction valve 3 to separation pump 4). Separation pump 4 may exhaust gases against atmospheric or near atmospheric pressure in a normal pressure region 36 from separation pump 4 to other abatement equipment/atmosphere as shown in FIG. 1 . Separation pump 4 may be a vacuum pump that is clean by design, namely that the vacuum pump does not introduce additional containments into the gaseous mixture. Separation pump 4 may include “dry” vacuum pumps, “oil-less” and “near-oil-less” vacuum pumps, and/or “diaphragm” vacuum pumps.

In some embodiments of the present disclosure, ETO condenser 50 may include a shell-tube, plate or other type of heat exchanger which may be cooled by coolant or refrigerant. ETO condenser 50 may condense and trap ETO vapors as well as other desirable dilutant such as CO₂, while allowing non-condensable (Mutant such as nitrogen (N₂), to pass through to the other abatement equipment atmosphere.

In some embodiments of the present disclosure, ETO condenser 50 may chill the gas mixture to a predefined temperature of about −110 deg C. (e.g., slightly higher than the ETO) melting point temperature of −112 deg C.) for condensing the ETO into an ETO vapor. The ETO vapor may include CO₂. ETO tank 500 may be used to store the condensed ETO (and CO₂ mixture, it any) until reuse. An ETO discharge valve 501 may be used to discharge ETO (and CO₂ mixture, if any) for reuse.

The following embodiments shown in FIGS. 2-6 schematically illustrate modifications to the basic system configuration shown in FIG. 1 for improving the system energy efficiency and throughput while recovering a sterilization agent such as ETO from a waste gaseous mixture output front the sterilization chamber.

FIG. 2 schematically illustrates a block diagram of a second embodiment of a system 15 for recovering a sterilization agent from a waste gaseous mixture, in accordance with some embodiments of the present disclosure. System 15 may include the same elements of system 10 as shown in FIG. 1 . However, the difference between system 10 and system 15 is that system 15 may include an H₂O freezer 31 after H₂O condenser 30, and an ETO freezer 51 after ETO condenser 50. H₂O freezer 31 and/or ETO freezer 51 are heat exchangers.

H₂O Freezer 31 may be a shell-tube, plate or other type of heat exchanger, cooled by chilled water, a coolant, or a refrigerant, which may further trap residual water vapor in the gaseous mixture that may have passed through H₂O condenser 30 by freezing the molecules to a surface of H₂O Freezer 31. H₂O Freezer 31 may allow clean ETO gas, together with other inert gases, such as nitrogen, to pass through.

Similarly, ETO Freezer 51 may be shell-tube, plate or other types, cooled by a coolant, a compressed refrigerant, or liquid gas type refrigerant, such as liquid nitrogen, for example, which may further trap residual ETO vapor and condensable dilutants such as CO₂ vapors, that have passed through ETO condenser 50 by freezing the molecules to a surface of ETO Freezer 51. ETO Freezer 51 may allow clean nitrogen gas to pass through an atmospheric exhaust valve 6 to the atmosphere.

FIG. 3 schematically illustrates a block diagram of a third embodiment of a system 20 for recovering a sterilization agent from a waste gaseous mixture, in accordance with some embodiments of the present disclosure. System 20 may include the same elements of system 15 as shown in FIG. 2 . However, the difference between system 15 and system 20 is that between separation pump 4 and ETO condenser 50, system 20 may include an after cooler 40 coupled to separation pump 4 followed by an exhaust warmer 61 and an ETO pre-condenser 50 a coupled to ETO condenser 50. Similarly, an ETO freezer economizer 60 may be coupled between ETO) condenser 50 and ETO Freezer 51. Exhaust warmer 61 may also be coupled to ETO freezer economizer 60 and to atmospheric exhaust valve 6.

After cooler 40 may be a heat exchanger that may be used to cool the hot compressed gas from separation pump 4 using cold water, for example. ETO Pre-condenser 50 a may include one or more heat exchangers that may be placed before and coupled to ETO condenser 50 so as to provide progressive stages of cooling the gas mixture so as to reduce the heat loading on ETO condenser 50.

ETO Freezer Economizer 60 may be a heat exchanger that pre-cools and pre-freezes the gaseous mixture entering ETO Freezer 51 using cooling energy from the exhaust gas of ETO Freezer 51.

Exhaust warmer 61 may be a heat exchanger used for pre-cooling and pre-condensing the gaseous mixture entering the ETO pre-condensers using cooling energy from the exhaust gas of ETO Freezer Economizer 60 and pre-warms the exhaust gas to near ambient temperature before venting the gas to the atmosphere is atmospheric exhaust valve 6.

FIG. 4 schematically illustrates a block diagram of a fourth embodiment of a system 22 for recovering a sterilization agent from a waste gaseous mixture, in accordance with some embodiments of the present disclosure. System 22 may include the same elements of system 15 as shown in FIG. 2 . However, system 22 may include one or more H₂O freezers and one or more ETO freezers connected in parallel. This may be shown schematically in FIG. 4 as two H₂O freezers 31 and 31′ and ETO Freezers 51 and 51′ connected in parallel.

In some embodiments of the present disclosure, one of the H₂O freezers (e.g., H₂O freezer 31) may be performing the freezing operation, while the other H₂O freezer (e.g., H₂O freezer 31′) may be thawed out or defrosted in order to prevent a build-up of solid ice on any one of the H₂O freezer surfaces. Similarly, one of the ETO freezers e.g., ETO freezer 51) may be performing the freezing operation, while the other ETO freezer (e.g., ETO freezer 51′) may be thawed out in order to prevent a build-up of solid ETO on any one of the H₂O freezer surfaces.

In some embodiments of the present disclosure, control and/or release valves may be placed before and/or after each of the two freezers that may be placed in parallel which may be used to control which freezer may route and cool the gaseous mixture while the other freezer is defrosting or de-thawing. In this manner, the entire process does not need to be halted so as to remove solid water ice and/or solid ETO by using the ETO and/or H₂O parallel freezers.

FIG. 5 schematically illustrates a block diagram of a fifth embodiment of a system 24 for recovering a sterilization agent from a waste gaseous mixture, in accordance with some embodiments oldie present disclosure. System 24 may include all of the elements of systems 20 and 24 shown in the previous FIGS. 3-4 with additional elements for further improving the energy efficiency relative to the previous figures.

The following description uses the system embodiments shown in FIG. 5 for providing a summary of the processes highlighting the different steps for recovering a sterilization agent from a waste gaseous mixture from sterilization chamber 1 in accordance with some embodiments of the present disclosure. All or part of these steps described hereinbelow may be applicable to each of the figures described herein:

-   -   1. The objects and/or items and/or products to be sterilized may         be placed in sterilization chamber 1. A gas mixture including         H₂O vapor, ETO with N₂ (and CO₂, if any) may be introduced into         sterilization chamber 1 through conduits (not shown in FIG. 5 )         while pressure reducing valve 3 is in a closed position.     -   2. During the period of sterilizing the objects and/or items         and/or products in sterilization chamber 1, H₂O Condenser 30,         H₂O Freezers 31 and 31′, After Cooler 40, ETO Pre-Condenser 50         a, ETO Condenser 50 and/or ETO Freezers 51 and 51′ may be each         pre-cooled to a predefined temperature.     -   3. H₂O Discharge Valve 301, ETO Discharge Valve 501, and Vacuum         Release Valve 302 may be placed in a closed position. An H₂O         Tank Isolation Valve 303 may be opened while one of H₂O Freezer         Release Valves 31 a or 31′a may be opened while the other         remains closed. Similarly, one of ETO Freezer Release Valves 51         a or 51′a may be opened while the other remains closed.         Atmospheric Exhaust Valve 6 may be opened. Separation Pump 4 may         then be activated causing the pressure inside reduced pressure         region 35 to drop to lower pressure vacuum conditions. Exhaust         in the system 24 may be vented through atmospheric exhaust valve         6 to the atmosphere, which keeps the pressure within the         elements of normal pressure region 36 at or near atmospheric         pressure.     -   4. After sterilization is completed, chamber evacuation pump 2         may be activated, and pressure reducing valve 3 may be opened so         as to allow the waste gas from sterilizing chamber 1 to flow         into H₂O Condenser 30. By varying how much pressure reducing         valve 3 is opened, or by varying the speed of separation pump 4,         or by varying both, the vacuum inside reduced pressure region 35         may be regulated and may be maintained at a predefined pressure,         in some embodiments without the use of H₂O freezers, the         predefined pressure may be in the range of 10 to 0.1 psi. In         other embodiments using H₂O freezers, the predefined pressure         may be in the range of 4 to 0.1 psi.     -   5. At the predefined pressure level, waste gas may flow into H₂O         Condenser 30, which was maintained at a predefined temperature.         Upon contacting the cooling surfaces of H₂O Condenser 30, H₂O         vapor in the stream of the waste gaseous mixture may condense         into liquid form, while the ETO, N₂ and CO₂ molecules in the         gaseous mixture stream of waste gas are not condensed at this         predefined temperature and remain in gaseous form within the         gaseous mixture. Therefore, the condensed H₂O liquid may be         separated from the remaining gases and collected by H₂O Tank         300. Other high boiling point contaminates, such as lubricating         oil mist generated by chamber evacuation pump 2, or polymers         formed hum the ETO, may also be separated from the waste gas         stream by H₂O Condenser 30. These contaminates may also be         collected in H₂O Tank 300.     -   6. The remaining stream of the gaseous mixture may exit from H₂O         condenser 30 into H₂O freezer 31 or 31′, whichever precedes the         opened H₂O Freezer Release Valve 31 a or 31 a′. H₂O Freezers 31         and 31′ have been maintained at predefined temperatures, below         the freezing point of H₂O but above the boiling point of ETO at         a predefined pressure. Upon contacting the cooling surfaces of         Freezer 31 or 31 a, the remaining water vapor in the gas stream         may freeze on these cooling surfaces, further reducing the         amount of water vapor in the gaseous mixture.     -   7. Whenever the cooling surfaces of either H₂O Freezer 31 and         31′ accumulate too much solid H₂O, and the thickness of the ice         is thick enough in one of the freezers so as to inhibit proper         heat transfer and efficient H₂O removal from the gas stream         (e.g., the gaseous mixture), then freezer release valve 31 a or         31 a′ of the inefficient freezer may be closed while the other         Freezer Release Valve remains opened.     -   8. As the gas stream is routed to the other H₂O Freezer, H₂O         removal from the gas stream may continue inside the         still-operating efficient freezer. Cooling inside the         inefficient freezer with too much ice build-up may be turned         off, while defrosting heaters on or near the cooling surfaces         may be turned on, so a to melt the solid ice that has built up         on the cooling surfaces of the inefficient Freezer back into         liquid form. In other embodiments, warm fluid may be pumped into         warm the cooling surfaces. This liquid, mainly water, may flow         into and be further collected by H₂O Tank 300 via H₂O Tank         isolation Valve 303. When the ice-melting and defrosting mock of         the inefficiently-operating freezer has been completed, (e.g.,         its cooling surfaces cleared of ice built-up), the defrosting         heaters may be turned off and cooling may resume to cool the         Freezer back to its predefined temperature. When the other         Freezer has accumulated too much ice built-up, the same         ice-removal steps can be repeated to defrost ice from its         cooling surfaces. In this manner, efficient H₂O removal from the         gas stream may be maintained without having to stop the entire         process in system 24 for ice-removal in the cooling elements.     -   9. Whenever H₂O Tank 300 is full, H₂O tank isolation valve 303         may be closed and vacuum release valve 302 may be opened to         allow the pressure inside the H₂O Tank 300 to return atmospheric         pressure. After that, H₂O Discharge Valve 301 may be opened to         discharge the contents of H₂O Tank 300. After discharge, valves         301 and 302 may be closed, and valve 303 may be opened. H₂O Tank         300 may then continue to receive condensate from H₂O Condenser         30 and H₂O Freezers 31 and 31′. In this manner, H₂O Tank 300 may         be discharged completely while waste gas removal from         Sterilization Chamber 1 may continue without interruption.     -   10. The remaining stream of waste gas mixture now free of H₂O         vapor may exit from H₂O Freezers 31 and 31′. The remaining         stream of waste gas mixture may include ETO vapor, N₂ and CO₂         gas, and pass through corresponding H₂O Freezer Release Valve 31         a or 31 a′, to separation pump 4 for compression to atmospheric         or near-atmospheric pressure.     -   11. The compression process by separation pump 4 increases the         gas stream temperature to above room temperature. The hot gas         stream may then enter ETO After Cooler 40, a heat exchanger         cooled by regular cooling water may be used to cool the gaseous         mixture to near room temperature.     -   12. After being cooled by ETO After Cooler 40, the near-room         temperature gas stream may enter an Exhaust Warmer 61. Exhaust         Warmer 61 may be a heat exchanger that warms the final cold         exhaust gas (e.g., after ETO removal) to near-room, temperature         before being released into the atmosphere. It may also be used         to recover expensive cooling energy from that cold exhaust gas,         to pre-cool the gas stream, and to pre-condense some of the ETO         vapor inside the gas stream. This conserved energy may be used         to cool ETO Pre-Condenser 50 a.         -   Since the freezing point of ETO is extremely low (−112             degrees C.), ETO Condenser 50 is cooled to extremely low             temperatures. In order to reduce heat load to ETO Condenser             so (e.g., increase cooling efficiency), and to provide more             effective condensing of the ETO vapor in the gaseous             mixture. ETO Pre-Condenser 50 a was placed before ETO             Condenser 50 as shown in FIG. 5 , which is not by way of             limitation of the embodiments of the present disclosure. One             or more pre-condensers may be placed in series before ETO             Condenser 50. ETO Pre-Condensers may each pre-cooled to             respective predefined temperatures such that each             Pre-Condenser may be progressively colder (e.g., at lower             temperatures) as they are positioned closer to ETO Condenser             50, with ETO Condenser 50 being the coldest (e.g., at the             lowest temperature).         -   As the gas stream exits from Exhaust Warmer 61 and enters             ETO Pre-Condenser 50 a, the gas stream may be pre-cooled and             the ETO vapors may be pre-condensed passing through the ETO             Pre-Condenser 50 a. Similarly, if a series of ETO             Pre-Condensers may be placed before ETO Condenser 50, the             gas stream may be progressively cooled, with ETO vapors             progressively condensed as the gas stream passes through             each of ETO Pre-Condensers in series. By pre-cooling the gas             stream in one single stage, or progressively pre-cooling the             gas stream in multiple stages of progressively colder             temperatures, the cooling system using Pre-Condensers is a             more energy efficient cooling system to cool the ETO             extremely low temperatures by using a series of             Pre-Condensers so as to stagger the temperatures to             progressively lower temperatures, yet higher than the             temperature of the final ETO Condenser 50. Thus, the total             energy needed to cool the gas stream was reduced, while             still cooling the gas stream, to the same low temperature.     -   13. ETO Condenser 50 may be pre-cooled and maintained at a         predefined temperature as the gas stream enters ETO Condenser         50. Inside ETO Condenser 50, ETO vapor may be condensed into         liquid form and was separated from the stream of the gaseous         mixture. The ETO then be collected by ETO Tank 500.         -   Note that if CO₂ gas is present in the remaining gas stream             from, separation pump 4, it will also be frozen into solid             form on the cooling surfaces of ETO Pre-Condenser 50 a and             ETO Condenser 50. CO₂ gas may be dissolved in the ETO liquid             condensate and collected in ETO Tank 500. However, N₂ gas in             the gas mixture will not be condensed nor frozen at the             predefined temperatures of ETO Pre-Condenser 51′ or ETO             Condenser 50. Therefore, N₂ gas may be separated from the             ETO condensate and CO₂ ice.     -   14. After condensable ETO vapor was removed from the gas stream         by ETO Pre-Condensers 50 a and ETO Condenser 50, the gas stream         may enter ETO Freezer Economizer 60 or 60′, whichever had a         corresponding ETO Freezer Release Valve 51 a or 51 a′ opened.         ETO Freezer Economizer 60 and 60′ may be a heat exchanger that         utilizes the cooling energy from the cold exhaust of ETO         Freezers 51 and 51′ to pre-cool the gas stream before entering         ETO) Freezers 51 and 51′.     -   15. ETO Freezer 51 and 51′ may be pre-cooled to a predefined         temperature (e.g., in a range of −112 deg C. to −196 deg C.),         below the freezing point of ETO) and above the boiling point of         N₂. After the gas stream enters ETO Freezers 51 and 51′, the         remaining ETO vapor in the gas stream may freeze onto the         cooling surfaces of the ETO Freezers where the ETO may be         separated from the gas stream. Consequently, ETO content in the         gas stream may be reduced to a minimum level.     -   16. The gas stream exiting ETO Freezers 51 and 51′ may include         N₂ gas free of environmentally harmful ETD (e.g., reduced to         sub-ppm levels of ETO). With all of the contaminates removed         from the gaseous mixture, the remaining clean gas is extremely         cold, and the valuable cooling energy of the N₂ gas may be         recovered in system 24.         -   The cold N₂ gas exiting ETO Freezers 51 and 51′ may be             coupled into corresponding ETO Freezer Economizers 60 and             60″, which are heat exchangers. The cold N₂ gas from ETO             Freezers 51 and 51′ may be used as a cooling medium that may             be fed back to cool ETO Freezer Economizers 60 and 60′,             which may subsequently be used to cool the gas stream             entering the inlets of ETO Freezers 51 and 51′.     -   17. Since the temperature of the N₂ gas is below the freezing         point of ETO, ETO Freezer Economizers 60 and 60′ may have solid         ETO frozen onto the cooling surfaces of the Economizer. Whenever         the cooling surfaces of either ETO Freezer Economizer 60 and ETO         Freezer 51, or ETO Freezer Economizer 60′ and ETO Freezer 51′         cooling surfaces may accumulate too much solid ETO, such that         the thickness of the solid ETO may inhibit proper heat transfer         and efficient ETO removal from the gas stream, then the         corresponding ETO Freezer Release Valve 51 a or 51 a′ may be         closed while the other ETO Freezer Release Valve remains open.         As the gas stream may be routed to the other ETO Freezer         Economizer and ETO Freezer, ETO removal from the gas stream may         continue.         -   Cooling may be turned off in the ETO Economizer and ETO             Freezer with too much solid ETO build-up, and heating             applied to the cooling surfaces was turned on. The solid ETO             that accumulated on the cooling surfaces of the ETO             Economizer and ETO Freezer may be defrosted back into ETO             liquid which may be collected by ETO Tank 500. In other             embodiments, warm fluid may be pumped into warm the cooling             surfaces. When ETO Economizer and ETO Freezer have been             completed defrosted, heating may then be turned off and the             cooling process restored, so as to cool the ETO Freezer back             to its predefined temperature. Similarly, when the other ETO             Freezer has accumulated too much. ETO solid built-up, the             same solid ETO removal steps may be repeated to clean the             cooling surfaces.     -   18. The cold N₂ gas stream passing through ETO Freezer         Economizer 60 or 60′ may be used to transfer its cooling energy         to other cooling elements in the system. For example, it may be         passed though the corresponding ETO Freezer Release Valve 51         a/51 ′a. This cold N₂ gas may be routed to Exhaust Warmer 61, so         as to pre-cool the gas stream that was about to enter ETO         Pre-Condensers 50 a. This process may warm the clean N₂ gas to         near room temperature as the N₂ gas cools the gas stream.         Therefore, reducing the amount of energy needed to cool the ETO         Pre-Condensers.     -   19. Whenever the contents of ETO Tank 500 may be discharged, ETO         discharge valve 501 may be opened. Since the pressure inside ETO         Tank 500 may be at or near atmospheric pressure, pure ETO stored         inside ETO Tank 500 may flow out without interrupting gas         removal from Sterilization Chamber 1.     -   20. After removal of the waste gas from Sterilization Chamber 1         is completed, Pressuring Reducing Valve 3 and Freezer Release         Valves 31 a and 31 ′a may be closed. Chamber Evacuation Pump 2         and Separation Pump 4 may be turned off.     -   21. In reduced pressure region 35, after ice may be removed from         H₂O Freezers 31 and 31′, and all condensates collected in H₂O         Tank 300, valve 303 may be closed and Vacuum Release Valve 302         may be opened so as to break the vacuum equalizing the pressure         inside H₂O Tank 300 with atmospheric pressure. H₂O Discharge         Valve 301 may be opened to allow the contents of H₂O Tank 300 to         flow freely from the tank. The discharged contents from H₂O Tank         300 may include clean water with slight oil mists from Chamber         Evacuation Pump 2 and traces of ETO polymers. This water may be         easily filtered and disposed of.     -   22. In normal pressure region 36, after Chamber Evacuation Pump         2 and Separation Pump 4 are turned off, ETO Freezer Release         Valve 51 a and 51 ′a may be closed to prevent ETO vapor to         escape into the atmosphere during ETO solid melting process in         all of the cooling elements. Then, cooling of ETO Freezers 51         and 51′ may be turned off and heating of the ETO Freezers 51 and         51′ and ETO Freezer In other embodiments, warm fluid may be         pumped into warm the cooling surfaces. Economizers 60 and 60′         may be turned on. Solid ETO that collected on surfaces of ETO         Freezers 51 and 51′, and ETO Freezer Economizers 60 and 60′ may         melt back into liquid ETO, which may be collected by ETO Tank         500 for reuse.     -   23. After inching of solid ETO has been completed, heating of         the ETO Freezers 51 and 51′ and ETO Freezer Economizers 60 and         60′ may be turned off, ETO Discharge Valve 501 may be opened to         allow the contents of ETO Tank 500 to be discharge for re-use.         Since the pressure inside normal pressure region 36 may be at or         near atmospheric pressure, the contents of ETO Tank 500 may flow         freely from ETO Tank 500, the contents of Tank 500 may include         pure ETO, free of water and other contaminates. In some cases,         the content may be a mixture of ETO and CO₂ if that was the         mixture used in Sterilization Chamber 1. This mixture is also         clean and free from water and other contaminates. The pure ETO,         or clean ETO/CO₂ mixture, after being discharged from Tank 500,         may be re-used in future processes.

The process for recovering and/or purifying a sterilization agent from a waste gas mixture as described hereinabove is not be way of limitation of the embodiments of the present disclosure. All or any steps of this process may be used in an of the FIGS. 1-6 shown herein in any suitable combination or order. The sterilization agent is not limited herein to ETO but may include other sterilization agents such as propylene oxide, for example.

FIG. 6 schematically illustrates a block diagram of a sixth embodiment of a system 26 for recovering a sterilization agent from a waste gaseous mixture, in accordance with some embodiments of the present disclosure. System 26 may include elements of system 15. However, the waste gaseous mixture processed by system 26 may be the waste gas from one or more sterilization chambers, denoted sterilization chamber 1, sterilization chamber 1′, and sterilization chamber 1″. Each of the one or more sterilization chambers may include respective one or more evacuation pumps denoted chamber evacuation pump chamber evacuation pump 2′, and chamber evacuation pump 2″ and one or more respective chamber waste gas exhaust valves denoted chamber waste gas exhaust valve 7, chamber waste gas exhaust valve 7′, and chamber waste gas exhaust valve 7″.

The waste gas from each of the one or more sterilization chambers may pass into a waste holding tank 700 and then coupled into the reduce pressure region 35 via pressure reducing valve 3 and normal pressure region 36 for recovering the ETO sterilization agent from the waste gas from the one or more sterilization chambers. Stated differently, the waste gases from the multiple sterilization chambers may be processed by a single sterilization agent recovery/process system as shown in FIG. 6 . Waste holding tank 700 may be of a variable volume so that pressure in the tank may be kept at atmospheric pressure, or a fixed volume type of tank.

FIG. 7 is a flowchart depicting a method 400 for recovering, a sterilization agent from a waste gaseous mixture, in accordance with some embodiments of the present disclosure.

Method 400 may include receiving 405 a waste gas from a sterilization chamber. The waste gas may include a gaseous mixture of a sterilization agent, nitrogen gas, and water vapor.

Method 400 may include reducing 410 a pressure of the gaseous mixture to a first predefined pressure so as to reduce a boiling point temperature of the sterilization agent to below a freezing point temperature of the water vapor in the gaseous mixture.

Method 400 may include cooling 415 the gaseous mixture with the pressure at the first predefined pressure to a temperature below a boiling point temperature and above the freezing point temperature of the water vapor, and removing condensed water vapor from the gaseous mixture.

Method 400 may include raising 420 the pressure of the gaseous mixture to a second predefined pressure greater than the first predefined pressure so as to elevate a boiling point temperature of the sterilization agent in the gaseous mixture.

Method 400 may include cooling 425 the gaseous mixture at the second predefined pressure to a temperature below the boiling point temperature and above a freezing point temperature of the sterilization agent causing the sterilization agent to condense into a liquid.

Method 400 may include separating 430 the liquid sterilization agent from the gaseous mixture so as to recover the sterilization agent for reuse from the waste gas.

Method 400 may include discharging 435 the nitrogen gas remaining in the gaseous mixture to the atmosphere or collecting the nitrogen gas for reuse.

In some embodiments of the present disclosure, a system for recovering a sterilization agent from a waste gaseous mixture may include a pressure reducing valve for reducing a pressure of a waste gas from one or more sterilization chambers to a first predefined pressure. The waste gas may include a gaseous mixture of a sterilization agent, nitrogen gas, and water vapor. A first condenser may be configured to receive the gaseous mixture via the pressure reducing valve, and to cool the gaseous mixture to a temperature below a boiling point temperature and above a freezing point temperature of the water vapor at the first predefined pressure. A first tank, coupled to the first condenser, may store the condensed water vapor separated from the gaseous mixture in the first condenser. A separation pump coupled to the first tank may raise the pressure of the gaseous mixture to a second predefined pressure. A second condenser may be configured to receive the gaseous mixture from the separation pump, to cool the gaseous mixture to a temperature below a boiling point temperature and above a freezing point temperature of the sterilization agent at the second predefined pressure causing the sterilization agent to condense into a liquid, and to discharge the nitrogen gas remaining in the gaseous mixture. A second tank, coupled to the second condenser, may store the sterilization agent separated from the gaseous mixture in the second condenser.

In some embodiments of the present disclosure, the sterilization agent may include ethylene oxide (ETO).

In some embodiments of the present disclosure, the first predefined pressure may be 1 pound per square inch and the second predefined pressure is atmospheric pressure.

In some embodiments of the present disclosure, the boiling point temperature of the water vapor may be 20 deg C. when the pressure of the gaseous mixture is 1 psi.

In some embodiments of the present disclosure, boiling point temperature of the ETO may be 10 deg C. when the pressure of the gaseous mixture is atmospheric pressure.

In some embodiments of the present disclosure, the sterilization agent may be propylene oxide.

In some embodiments of the present disclosure, the system may include a chamber evacuation pump coupled to the pressure reducing valve for pumping the waste gas into the first condenser.

In some embodiments of the present disclosure, the system may include an exhaust warmer and a freezer economizer for recovering cooling energy in the system.

In some embodiments of the present disclosure, the system may include one or more H₂O freezers coupled to the first condenser and the separation pump, and wherein each of the one or more H₂O freezers may freeze H₂O molecules in the water vapor to a freezer surface.

In some embodiments of the present disclosure, at least two H₂O freezers from the one or more H₂O freezers may be connected in parallel coupled between the first condenser and the separation pump.

In some embodiments of the present disclosure, the system may include an ETO freezer coupled to the second condenser for trapping residual vapors of the sterilization agent.

In some embodiments of the present disclosure, the system may include a waste gas holding tank coupled to the pressure reducing valve and to the one or more sterilization chambers for collecting the waste gas from the one or more sterilization chambers.

In some embodiments of the present disclosure, the system may include one or more ETO pre-condensers placed in series before the second condenser, wherein each of the one or more pre-condensers may have progressively lower temperatures above the temperature of the second condenser.

In some embodiments of the present disclosure, a method for recovering a sterilization agent from a waste gaseous mixture may include receiving a waste gas from a sterilization chamber. The waste gas may include a gaseous mixture of a sterilization agent, nitrogen gas, and water vapor, A pressure of the gaseous mixture may be reduced to a first predefined pressure so as to reduce a boiling point temperature of the sterilization agent to below the freezing point temperature of the water vapor in the gaseous mixture. The gaseous mixture with the pressure at the first predefined pressure may be cooled to a temperature below a boiling point temperature and above the freezing point temperature of the water vapor. Condensed water vapor may be removed from the gaseous mixture. The pressure of the gaseous mixture may be raised to a second predefined pressure greater than the first predefined pressure so as to elevate a boiling point temperature of the sterilization agent in the gaseous mixture. The gaseous mixture at the second predefined pressure may be cooled to a temperature below the boiling point temperature and above a freezing point temperature of the sterilization agent causing the sterilization agent to condense into a liquid. The liquid sterilization agent may be separated from the gaseous mixture so as to recover the sterilization agent for reuse from the waste gas. The nitrogen gas remaining in the gaseous mixture may be discharged.

In some embodiments of the present disclosure, the sterilization agent may include ethylene oxide (ETO).

In some embodiments of the present disclosure, the first predefined pressure may be 1 pound per square inch (psi) and the second predefined pressure may be atmospheric pressure.

In some embodiments of the present disclosure, the boiling point temperature of the water vapor may be 20 deg C. when the pressure of the gaseous mixture is 1 psi.

In some embodiments of the present disclosure, the boiling point temperature of the ETO may be 10 deg C. when the pressure of the gaseous mixture is atmospheric pressure.

In some embodiments of the present disclosure, the sterilization agent may be propylene oxide (PO).

In some embodiments of the present disclosure, discharging the nitrogen gas may include discharging the nitrogen gas to the atmosphere or collecting the discharged nitrogen gas for reuse.

In some embodiments of the present disclosure, the method may include recovering cooling energy in the system by using an exhaust warmer and a freezer economizer.

In some embodiments of the present disclosure, the method may include freezing H₂O molecules in the water vapor to a freezer surface of one or more H₂O freezers.

In some embodiments of the present disclosure, at least two H₂O freezers from the one or more H₂O freezers may be connected in parallel, and the method may include defrosting at least one of the H₂O freezers horn the at least two parallel H2O freezers.

In some embodiments of the present disclosure, the method may include trapping residual vapors of the sterilization agent using one or more ETO freezers coupled to the second condenser

In some embodiments of the present disclosure, at least two ETO freezers from the one or more H₂O freezers may be connected in parallel, and the method may include defrosting at least one of the ETO freezers from the at least two parallel ETO freezers.

In some embodiments of the present disclosure, the method may include collecting the waste gas from the one or more sterilization chambers in a waste gas holding tank.

In some embodiments of the present disclosure, the method may include setting the temperatures of each of one or more ETO pre-condensers placed in series before the second condenser to progressively lower temperatures above the temperature of the second condenser.

In case there is more than one sterilization chambers that exhaust waste gas, thereby creating a large stream waste gas flow, an increase in the size of each of the elements of a sterilization agent recovering system and thereby an increase in the size of the entire sterilization agent recovering system would typically be required.

A size increase of the recovering system would incur an increase in the space occupied by the system, which is usually already restricted, as well as an increase in installation and operation costs.

The cost of operation is increased to handle an increased waste gas flow coming from more than one sterilization chambers, especially due to the cost of cooling required to cool the condensers, and especially for cooling the condensers and the freezer(s), if such freezer(s) are at all implemented in the system.

The increase in cost of cooling is due to the increased amount of gaseous sterilizing agent in the waste gas stream, but also due to the increased amount of dilution gas(es), e.g., N₂ and possibly CO₂, which are present in the waste gas stream.

The problem of increased cooling energy is even worsened by the fact that, in cooling systems, the cost of cooling drastically increases as the intended temperature decreases. For example, in one embodiment, one of the condensers may be cooled as low as minus 110 degrees Celsius. The cost to cool the condenser to this low temperature costs about ten times more than it is to cool another condenser of the system, which operates at about 4 degrees Celsius.

Accordingly, the present disclosure provides a recovering system that includes a gas separator and in some embodiments a gas evaporator. A gas separator and possibly a gas evaporator are introduced after the exhaust pumps of one or more sterilization chambers and before the pressure reducing valve of the system for recovering a sterilization agent, which is schematically illustrated in FIG. 1 .

FIG. 8 schematically illustrates a block diagram of an embodiment of a system 80 for recovering a sterilization agent from a waste gaseous mixture from one or more sterilization chambers, in accordance with some embodiments of the present disclosure.

System 80 may include one or more sterilization chambers 1 each coupled to a H₂O tank 300 (also known herein as a first tank), a H₂O condenser 30 (also known herein as a first condenser) and an ETO condenser 50 (also known herein as a second condenser). H₂O condenser 30 may be coupled to H₂O tank 300, and ETO condenser 50 may be coupled to ETO tank 500 (also known herein as a second tank). H₂O tank 300 and ETO tank 500 may be respectively used for storing the H₂O liquid and ETO during and/or after their separation process. In some embodiments, the gaseous mixture of waste gas from one or more sterilization chambers 1 may be pumped into gas separator 82 using a chamber evacuation pump 2.

Thus, system 80, unlike system 10 is designed such that the waste gas mixture from the one or more sterilization chambers 1 first enters H₂O tank 300, while H₂O condenser 30 that is coupled to H₂O tank 300 is only reached after passage through H₂O tank 300.

In addition, system 80 farther comprises a gas separator 82, coupled to the one or more sterilization chambers 1, e.g., via evacuation pump 2, and further coupled to H₂O tank 300, via pressure reducing valve 3.

In some embodiments, gas separator 82 may contain common water. The gas separator 82 may be configured to wash waste gas from one or more sterilization chambers 1, with water. As the waste gas comprises a gaseous mixture of a sterilization agent, nitrogen gas, and water vapor, the sterilization agent and water vapor may be absorbed by the water within gas separator 82, thereby creating a water-gaseous sterilization agent mixture that may be collected at a bottom section of gas separator 82, and the dilution gas, e.g., N₂ gas may be exhausted at a top section of gas separator 82.

Gas separator 82 may receive a large waste gas stream flow exhausting from the one or more sterilization chambers 1 via exhaust pumps, and may retain the waste as stream inside gas separator 82 for a period of time 0.1 to 10 minutes to increase the surface area which the waste gas comes in contact with the water contained in the gas separator 82. This allows water soluble and condensable components in the waste gas stream, in particular the gaseous sterilizing agent and water vapors, to be dissolved and condensed into the water, forming a water mixture that is rich in sterilization agent, i.e., a water-gaseous sterilization agent mixture. The water-gaseous sterilization agent mixture may then be collected at the bottom portion of the gas separator 82 or in a designated water mixture receiving tank (not shown). At the same time, the non-water soluble and non-condensable components in the waste gas stream, in particular the insert dilution gas(es), e.g., N₂ gas and possibly CO₂ gas, may be separated from the water-gaseous sterilization agent mixture, and may exit near the top section of the gas separator 82, and may then be exhausted into the atmosphere or to other abatement equipment.

According to some embodiments, gas separator 82 in elect separates the gaseous sterilization agent, e.g., ethylene oxide (ETO) or propylene oxide (PO) from the inert dilution gas(es), e.g., N₂ gas, CO₂ gas, or a combination of N₂ gas and CO₂ gas, by taking advantage of the differences in their solubility property in water. The gaseous sterilization agents are highly soluble in water, i.e., 100 grams ETO dissolve in 1 liter of water, and 400 g. PO dissolve in 1 liter of water at 20 degrees Celsius, while inert dilution gases are considered not soluble in water, as only 0.02 g of N₂ dissolve in 1 liter of water, and only 1.7 g of CO₂ dissolve in 1 liter of water, at the same temperature of 20 degrees Celsius. By retaining and interfacing the waste gas stream with water, the gas separator 82 may dissolve the sterilization agent from the waste gas stream into the water. That is, the clean water in gas separator 82 effectively wash the gas stream to thereby strip the waste gas stream of the sterilization agent and only leave clean dilution gas as part of the waste gas stream. The dilution gas, e.g., N₂ and possibly CO₂, may then be exhausted into the atmosphere or other abatement equipment through a top portion of gas separator 82, while the water-gaseous sterilization agent mixture may exit gas separator 82 through its bottom portion.

According to some embodiments, since system 80 exhausts the dilution gas, e.g., N₂ and possibly CO₂ gas at an early stage of the recovering process, i.e., the dilution gas exits system 80 from gas separator 82, system 80 need to treat the dilution gas throughout the entire system, as done, for example, in system 10. This early exhaustion of the dilution gas from the system leads to recovering system 80 being smaller compared to the basic recovering system 10 thereby system 80 consumes less space, and possibly less energy as the entire procedure is simpler, which are both important advantages of system 80.

In some embodiments, the recovering system may be even smaller, since the sterilization agent dissolved in water, i.e., the water-gaseous sterilization agent mixture, may be stored to be processed later by a recovering system. Thus, the one or more sterilization chambers 1, one or more evacuation pumps 2 and the gas separator 82 along with a water-gaseous sterilization agent mixture container, may be part of an initial separation system, which separates the dilution gas from the waste gas thereby leaving the sterilization agent dissolved in water, while the water-gaseous sterilization agent mixture may later be inputted into a recovering system, which is thus smaller than system 80.

In some embodiments, the water-gaseous sterilization agent mixture from the gas separator 82 can be stored at the lower part of the gas separator 82, stored in separate designated tanks, or may be directly connected to H₂O tank 300.

In some embodiments of the present disclosure, pressure reducing valve 3 may reduce the pressure of the water-gaseous sterilization agent mixture pumped into H₂O tank 300 to a first predefined value such as 1 psi (e.g., pound per square inch), for example, or any suitable pressure value, so as to reduce the boiling point temperature of the sterilization agent component in the water-gaseous sterilization agent mixture. The system elements operating at a reduced pressure are shown in reduced pressure region 35 (e.g., inside the dotted rectangle).

In some embodiments of the present disclosure, one or more sterilization chambers 1 may include an enclosure with the objects and/or items to be sterilized, configured to withstand pressure variances. One or more sterilization chambers 1 may include inlet and/or outlet ports for removing air, injecting sterilization agent gases, and removing waste gases.

In some embodiments of the present disclosure, chamber evacuation pump 2 may comprise vacuum pumps of various types, capable of removing the waste gas from one or more sterilization chambers 1. In some embodiments, when there is more than one sterilization chambers 1, each sterilization chamber may be coupled to a corresponding chamber evacuation pump 2.

In some embodiments of the present disclosure, system 80 may include pressure reduction valve 3 which may be a throttling valve, capable of reducing and maintaining system pressure in reduced pressure region 35.

In some embodiments, H₂O tank 300 may be heated to heat the water-gaseous sterilization agent mixture to a temperature above boiling, point temperature of the sterilization agent and above a freezing point temperature of the water to produce gaseous sterilization agent and water vapor.

In some embodiments of the present disclosure, H₂O condenser 30 may include a shell-tube, plate or other type of heat exchanger, which may be cooled by chilled water or refrigerants. H₂O condenser 30 may condense and trap water vapor and other contaminants, such as oil used by chamber evacuation pump 2. H₂O condenser 30 may also allow the clean gaseous sterilization agent to pass into ETO condenser 50.

The condensed water vapor may be received by H₂O tank 300, while H₂O tank 300 keeps on heating the water-gaseous sterilization agent mixture to maintain the process of separating the sterilization agent from the water vapor. The water-gaseous sterilization agent mixture is continuously heated by H₂O tank 300, which also collects condensed water vapor that is condensed by H₂O condenser 30, and gaseous sterilization agent is passed from H₂O condenser 30 to ETO condenser 50, until the entire amount of gaseous sterilization agent is passed into ETO condenser 50. The process of heating H₂O tank 300 is repeated until the entire amount of gaseous sterilization agent is removed from H₂O tank 300 into ETO condenser 50.

For example, assuming the percentage of dissolved water vapor in the water gaseous sterilization agent mixture is 50%, and the percentage of the dissolved gaseous sterilization agent is 50%, after H₂O tank 300 is heated to produce water vapor and some gaseous sterilization agent, the water vapor and gaseous sterilization agent enter H₂O condenser 30, in which water vapor is condensed and goes back into H₂O tank 300. During that same process, the gaseous sterilization agent is moved from H₂O condenser 30 to ETO condenser 50. Now, the water-gaseous sterilization agent mixture in H₂O tank 300 comprises 60% water and 40% gaseous sterilization agent since some of the sterilization agent has moved to ETO condenser 50. This new mixture is reheated within H₂O tank 300, to produce water vapor to be condensed by H₂O condenser 30, and some gaseous sterilization agent to be moved into ETO condenser 50, thereby reducing the percentage of the sterilization agent within H₂O tank 300 once again. This process repeats itself until H₂O tank 300 contains only water, while the entire amount of gaseous sterilization agent is present in ETO condenser 50.

In some embodiments, the ETO evaporation process performed by H₂O tank 300, comes to an end when the boiling temperature of the mixture within H₂O tank 300 starts to increase, e.g., from the boiling temperature of ETU it increases to the boiling temperature of water.

For a pressure of 1 psi, the boiling point of water may be reduced to 20 deg C., while the boiling, point of ETO is −45 deg C. H₂O condenser 30 may be a heat exchanger that chills the gas mixture to about 4 deg C. to condense the water vapor and contaminants from the sterilization process of the items and or objects in one or more sterilization chambers 1 such as oil, polymers formed by the sterilization agent, for example, that may be mixed into the water vapor.

An H₂O discharge valve 301 may be used to discharge H₂O and other contaminants stored in H₂O tank 300. A vacuum release valve 302 may be used to release the vacuum inside reduced pressure region 35 so as to allow the pressure inside H₂O tank 300 to equalize with the pressure outside of valve 301, so that the content of H₂O tank 300 can be discharged via gravity.

In some embodiments of the present disclosure, the gaseous sterilization agent with the water vapor removed in reduced pressure region 35, may be pumped into ETO condenser 50 by a separation pump 4 via a separation valve 4A, which separates reduced pressure region 35 in system 80 from normal pressure region 36 in system 80. Separation valve 4A may allow the gaseous sterilization agent to enter separation pump 4 which pumps the gaseous sterilization agent into ETO condenser 50 while raising the pressure of the gaseous sterilization agent to near atmospheric pressure.

In some embodiments of the present disclosure, separation pump 4 may include a vacuum pump capable of maintaining reduced pressures in reduced pressure region 35 (e.g., the region shown from pressure reduction valve 3 to separation pump 4). Separation pump 4 may exhaust gases against atmospheric or near atmospheric pressure in a normal pressure region 36 from separation pump 4 to other abatement equipment/atmosphere as shown in FIG. 8 . Separation pump 4 may be a vacuum pump that is clean by design, namely that the vacuum pump does not introduce additional containments into the gaseous sterilization agent. Separation pump 4 may include “dry” vacuum pumps, “oil-less” and “near-oil-less” vacuum pumps, and/or “diaphragm” an pumps.

In some embodiments of the present disclosure, ETO condenser 50 may include a shell-tube, plate or other type of heat exchanger which may be cooled by coolant or refrigerant. ETO condenser 50 may condense and trap sterilization agent vapors e.g., ETO vapors.

In some embodiments of the present disclosure, ETO condenser 50 may chill the gaseous sterilization agent to a predefined temperature of about −110 deg C. slightly higher than the ETO melting point temperature of −112 deg C.) for condensing the ETO into an ETO liquid. The ETO vapor may include CO₂. ETO tank 500 may be used to store the condensed ETO (and CO₂ mixture if any) until reuse. An ETO discharge valve 501 may be used to discharge ETO (and CO₂ mixture, if any) for reuse.

In some embodiments, the water in gas separator 82 may be replaced by Ethylene Glycol, or a mixture of water and Ethylene Glycol. In some embodiments, gas separator 82 may be cooled to cool the water, Ethylene Glycol, or water/Ethylene Glycol mixture to between 10 to −40 deg C., so that condensation and solubility of the sterilization agent, ETO, in the water, Ethylene Glycol or water/Ethylene Glycol mixture is further improved.

For typical sterilization chambers, the time it takes a sterilization chamber to exhaust ETO gas is between 15-30 minutes, while the whole sterilization cycle takes about 8-12 hours. For a system without the gas separator, the system's entire components need to be sized (e.g., enlarged) such to treat all of the exhaust waste stream from more than one sterilization chambers. However, for a system comprising a gas separator, the entire waste gas stream may be treated within 15-30 minutes by the large gas separator via washing the waste gas with water, separating the gaseous sterilization agent from the inert dilution gases and storing the gaseous sterilization agent in a liquid form of water-gaseous sterilization agent mixture. Thus, the rest of the recovering system can be smaller, compared to a recovering system with no gas separator, due to having all 8-12 hours of the sterilization cycle time to treat and separate ETO from the water-gaseous sterilization agent mixture.

FIG. 9 schematically illustrates a block diagram of an embodiment of a system for recovering a sterilization agent from a waste gaseous mixture from one or more sterilization chambers, in accordance with some embodiments of the present disclosure.

According to some embodiments, system 90 may differ from system 80 in that system 90 may further comprise an evaporator 92, which may be the component of system 90 designated to heat the water-gaseous sterilization agent mixture instead of H₂O tank 300 as in system 80. By having a designated component within system 90, that is configured to heat the water-gaseous sterilization agent mixture prior to separation of the water vapor from the sterilization agent, the energy of is increased, as there is no need for continuously reheating the mixture of water and sterilization agent within H₂O tank 300, until the sterilization agent is entirely separated from the condensed water that is continuously received by H₂O tank 300.

System 90 may include one or mote sterilization chambers 1 each coupled to a H₂O condenser 30 (also known herein as a first condenser), a H₂O tank 300 (also known herein as a first tank), and an ETO condenser 50 (also known herein as a second condenser). H₂O condenser 30 may be coupled to H₂O tank 300, and ETO condenser 50 may be coupled to ETO tank 500 (also known herein as a second tank), H₂O tank 300 and ETO tank 500 may be respectively used for storing the H₂O liquid and ETO during and/or after their separation process.

System 90 further comprises a gas separator 82, coupled to the one or more sterilization chambers 1, e.g., via evacuation pump 2, and further coupled to evaporator 92, e.g., via pressure reducing valve 3. In some embodiments, the gaseous mixture of waste gas from one or more sterilization chambers 1 may be pumped into gas separator 82 using a chamber evacuation pump 2.

In some embodiments, gas separator 82 may contain common water. The gas separator 82 may be configured to wash waste gas from one or more sterilization chambers 1, with water. As the waste gas comprises a gaseous mixture of a sterilization agent, nitrogen gas, and water vapor, the sterilization agent and water vapor may be absorbed by the water within gas separator 82, thereby creating a water gaseous sterilization agent mixture that may be collected at a bottom section of gas separator 82, and the dilution gas, e.g., N₂ gas, may be exhausted at a top section of gas separator 82.

Gas separator 82 may receive a large waste gas stream flow exhausting from the one or more sterilization chambers 1 via exhaust pumps, and may retain the waste gas stream inside gas separator 82 for a time of 0.1 to 10 minutes to increase the surface area which the waste gas comes in contact with the water contained in the gas separator 82. This allows water soluble and condensable components in the waste gas stream, in particular the gaseous sterilizing agent and water vapors, to be dissolved and condensed into the water, forming a water mixture that is rich in sterilization agent, i.e., a water-gaseous sterilization agent mixture. The water-gaseous sterilization agent mixture may then be collected at the bottom portion of the gas separator 82 or in a designated water mixture receiving tank (not shown). At the same time, the non-water soluble and non-condensable components in the waste gas stream, in particular the dilution gas, e.g., NZ and possibly CO₂ gas, may be separated from the water-gaseous sterilization agent mixture, and may exit near the top section of the gas separator 82, and may then be exhausted into the atmosphere or to other abatement equipment.

According to some embodiments, gas separator 82 in effect separates the gaseous sterilization agent, e.g., ethylene oxide (ETO) or propylene oxide (PO) from the dilution gas, e.g., N₂ gas and possibly CO₂ gas, by taking advantage of the differences in their solubility property in water. The gaseous sterilization agents are highly soluble in water, i.e., 100 grams ETO dissolve in 1 liter of water, and 400 g PO dissolve in 1 liter of water at 20 degrees Celsius, while dilution gases are considered not soluble in water, as only 0.02 g of N₂ dissolve in 1 liter of water, and only 1.7 g of CO₂ dissolve in 1 liter of water, at the same temperature of 20 degrees Celsius. By retaining and interfacing the waste gas stream with water, the gas separator 82 may dissolve the sterilization agent from the waste gas stream into the water. That is, the clean water in gas separator 82 effectively wash the gas stream to thereby strip the waste gas stream of the sterilization agent and only leave clean dilution gas as pan of the waste gas stream. The dilution gas, e.g., N₂ and possibly CO₂, may then be exhausted into the atmosphere or other abatement equipment through a top portion of gas separator 82, while the water-gaseous sterilization agent mixture may exit gas separator 82 through its bottom portion.

According to some embodiments, since system 90 exhausts the dilution gas, e.g., N₂ gas and possibly CO₂ gas, at an early stage of the recovering process, i.e., the dilution gas exits system 90 from gas separator 82, system 90 need to treat the dilution gas throughout the entire system, as done, for example, in system 10. This early exhaustion of the dilution gas from the system leads to recovering system 90 being smaller compared to the basic recovering system 10, thereby system 90 consumes less space, and possibly less energy as the entire procedure is simpler, which are both important advantages of system 90.

In some embodiments, the recovering system may be even smaller, since the sterilization agent dissolved in water, i.e., the water-gaseous sterilization agent mixture, may be stored to be processed later by a recovering system. Thus, the one or more sterilization chambers 1, one or more evacuation pumps 2 and the gas separator 82 along with a water-gaseous sterilization agent mixture container, may be part of an initial separation system, which separates the dilution gas from the waste gas thereby leaving, the sterilization agent dissolved in water, while the water-gaseous sterilization agent mixture may later be inputted into a recovering system, which is thus smaller than system 90.

In some embodiments, the water-gaseous sterilization agent mixture from the gas separator 82 can be stored at the lower part of the gas separator 82, stored in separate designated tanks, or may be directly connected to evaporator 92.

In some embodiments of the present disclosure, pressure reducing valve 3 may reduce the pressure of the water-gaseous sterilization agent mixture pumped into evaporator 92 to a first predefined value such as 1 psi (e.g., pound per square inch), for example, or any suitable pressure value, so as to reduce the boiling point temperature of the sterilization agent component in the water-gaseous sterilization agent mixture. The system elements operating at a reduced pressure are shown in reduced pressure region 35 (e.g., inside the dotted rectangle).

In some embodiments of the present disclosure, one or more sterilization chambers 1 may include an enclosure with the objects and/or items to be sterilized configured to withstand pressure variances. One or more sterilization chambers 1 may include inlet and/or outlet ports for removing air, injecting sterilization agent gases, and removing waste gases.

In some embodiments of the present disclosure, chamber evacuation pump 2 may comprise vacuum pumps of various types, capable of removing the waste gas from one or more sterilization chambers 1. In some embodiments, when there is more than one sterilization chambers 1, each sterilization chamber may be coupled to a corresponding chamber evacuation pump 2.

In some embodiments of the present disclosure, system 90 may include pressure reduction valve 3 which may be a throttling valve, capable of reducing and maintaining system pressure in reduced pressure region 35.

In some embodiments, an evaporator 92, which may be coupled to gas separator 2 via pressure reducing valve 3, may be heated to heat the water-gaseous sterilization agent mixture to a temperature above boiling point temperature of the sterilization agent and above a freezing point temperature of the water, to produce gaseous sterilization agent and water vapor. That is, system 90 has a designated component for heating the water-gaseous sterilization agent mixture to produce gaseous sterilization agent and water vapor, unlike system 80 in which H₂O tank 300 acts as an evaporator as well as a storage tank for storing water condensed by H₂O condenser 30.

In some embodiments of the present disclosure, H₂O condenser 30 may include a shell-tube, plate or other type of beat exchanger, which may be cooled by chilled water or refrigerants. H₂O condenser 30 may condense and trap water vapor and other contaminants, such as oil used by chamber evacuation pump 2, H₂O condenser 30 may also allow the clean gaseous sterilization agent to pass into ETO condenser 50.

The condensed water vapor may be received by H₂O tank 300 to be stored therein. For a pressure of 1 psi, the boding point of water may be reduced to 20 deg C., while the boiling point of ETO is −45 deg C. H₂O condenser 30 may be a heat exchanger that chills the gas mixture to about 4 deg C. to condense the water vapor and contaminants from the sterilization process of the items and/or objects in one or more sterilization chambers 1 such as oil, polymers formed by the sterilization agent, for example, that may be mixed into the water vapor.

An H₂O discharge valve 301 may be used to discharge H₂O and other contaminants stored in H₂O tank 300. A vacuum release valve 302 may be used to release the vacuum inside reduced pressure region 35 so as to facilitate discharging H₂O and other contaminants stored in H₂O tank 300. Vacuum release valve 302 may be located between H₂O condenser 30 and H₂O tank 300, between evaporator 92 and H₂O condenser 30, or at other locations along system 90.

In some embodiments of the present disclosure, the gaseous sterilization agent with the water vapor removed in reduced pressure region 35, may be pumped into ETO condenser 50 by a separation pump 4 via a separation valve 4A, which separates reduced pressure region 35 in system 90 from normal pressure region 36 in system 90. Separation valve 4A may allow the gaseous sterilization agent to enter separation pump 4 which pumps the gaseous sterilization agent into ETO condenser 50 while raising the pressure of the gaseous sterilization agent to near atmospheric pressure.

In some embodiments of the present disclosure, separation pump 4 may include a vacuum pump capable of maintaining reduced pressures in reduced pressure region 35 (e.g., the region shown from pressure reduction valve 3 to separation pump 4). Separation pump 4 may exhaust gases against atmospheric or near atmospheric pressure in a normal pressure region 36 from separation pump 4 to other abatement equipment/atmosphere as shown in FIG. 9 . Separation pump 4 may be a vacuum pump that is clean by design, namely that the vacuum pump does not introduce additional containments into the gaseous sterilization agent. Separation pump 4 may include “dry” vacuum pumps, “oil-less” and “near-oil less” vacuum pumps, and/or “diaphragm” vacuum pumps.

In some embodiments of the present disclosure, ETO condenser 50 may include a shell-tube, plate or other type of heat exchanger which may be cooled by coolant or refrigerant. ETO condenser 50 may condense and trap sterilization agent vapors, e.g., ETO vapors.

In some embodiments of the present disclosure, ETO condenser 50 may chill the gaseous sterilization agent to a predefined temperature of about −110 deg C. slightly higher than the ETO melting point temperature of −112 deg C.) for condensing the ETO into an ETO liquid. ETO tank 500 may be used to store the condensed ETO until reuse. An ETO discharge valve 501 may be used to discharge ETO for reuse.

In some embodiments, the water in gas separator 82 may be replaced by Ethylene Glycol, or a mixture of water and Ethylene Glycol. In some embodiments, gas separator 82 may be cooled to cool the water, Ethylene Glycol, or water-Ethylene Glycol mixture to between 10 to −40 deg C., so that condensation and solubility of the sterilization agent, ETO, in the water, Ethylene Glycol or water-Ethylene Glycol mixture is further improved.

In some embodiments, the water-gaseous sterilization agent mixture from gas separator 82 can be stored at the lower part of the gas separator 82, stored in separate designated tanks, may be directly connected to H₂O tank 300, or may be directly connected to evaporator 92.

In both of systems 80 and 90, the dilution gas, e.g., N₂ and CO₂, is exhausted out of either of these systems at the beginning of the recovering process, such that the gas stream entering the reduced pressure region 35 includes no dilution gas and only includes a water-gaseous sterilization agent mixture (i.e., condensable water vapor and gaseous sterilization agent). There are several benefits for removing the dilution gas at the beginning of the process instead of exhausting it at the end of the recovering process or even during the process at a later stage than that of gas separator 82, a few of them being

-   -   1. increasing efficiency of the condensers. Since the thermal         conductivity of the non-condensable dilution gas is extremely         low compared to that of the material of the heat transfer         surface in the condensers (specifically, 25 mW/(m*K) for N₂, 15         W/(m*K) for CO₂, compared to 15,000 mW/(m*K) for stainless steel         and 386,000 mW/(m*K) for copper, whereby mW/(m*K) means that for         every meter thickness of material at 1 Kelvin of temperature         difference between the hot side and cold side, heat can pass         through at a rate of 25 milliwatts). The non-condensable         dilution gas having very low thermal conductively may form a         boundary layer on the heat transfer surface of the condensers,         thereby to behave like an insulator and hinder the waste gas         stream from being further cooled and condensed by the condenser         heat transfer surface material. By removing the non-condensable         dilution gas from the Waste gas stream, the efficiency of the         condensers is greatly increased by as much as several orders of         magnitude. The result is that much smaller sized condensers may         be employed in either of systems 80 or 90.     -   2. Eliminating the need to cool the non-condensable dilution         gases to the very low temperature of the second condenser (e.g.,         ETO condenser 50). As implemented in either of systems 80 or 90,         after the water-gaseous sterilization agent mixture passes the         first condenser, e.g., H₂O condenser 30, the only gas remaining         in the gas stream mixture is the gaseous sterilization agent.         This reduces the total mass of the gas flow to the second         condenser, and thus reduces the cooling energy required to cool         the second condenser.     -   3. Eliminating the need to proportionally enlarge the         condensers, pump, and cooling systems to handle the larger peak         flow. By temporary retaining the gaseous sterilization agent in         the new water-gaseous sterilization agent mixture that is thus         rich with water soluble sterilization agent, the only component         that needs to be changed in size to handle the large peak flow         is the gas separator. e.g., gas separator 82, which may be         easily acquired at a reasonable cost. After the waste gas stream         passes through the gas separator, the gaseous sterilization         agent is dissolved in the water to produce a water-gaseous         sterilization agent mixture, such that the sterilization agent         is contained in liquid form. When the gaseous sterilization         agent is transformed from gas form to liquid form, the volume of         the gaseous sterilizing agent is reduced by 3 orders of         magnitude (e.g., from 1.67 liters/gram to 1.13 ml/gram), making         it easily storable in storage tanks. Storing the gaseous         sterilization agent in liquid form, enables continuing with the         recovering process at a later time, by generating a new gas         stream either by H₂O tank 300 in system 80, or by evaporator 92         in system 90. Thus, the rest of the system's components, that         are more expensive to acquire, do not need to be enlarged to         simultaneously handle the large peak flow generated by the         multiple large sterilization chambers 1. Rather, the condenser,         valves, corresponding cooling systems, and the separation pump,         may be sized to handle the “average” flow rate from the one or         more sterilization chambers 1. This is particularly advantageous         in terms of sizing reduction of the systems, since the normal         sterilization chamber operates in “batch” operations. In one         “batch” operation, or one sterilization cycle, the time of         exhausting waste sterilization gas only occupies 2˜4% of the         total operation time. With the ability to store the gaseous         sterilization agent in liquid form, it may be processed at a         later time in a steady, smaller and continuous rate. This means         that other than the gas separator, the rest of either of systems         80 or 90, may be sized to treat only 1/20 to 1/50 of the peak         gaseous sterilizing agent flow rate, which presents very         significant sizing reduction of either of the systems.

Therefore, the feature of the gas separator, which enables exhaustion of dilution gas at an early stage from the recovering system, as well as enables storing the sterilization agent in liquid form for later process, provides the sizing and the initial capital cost of acquiring and installing either of systems 80 or 90 to handle large peak flows from multiple sterilization chambers to be significantly reduced to a fraction of what it would have been without the new gas separator feature.

In addition, with this new gas separator feature, the operational cost of either of systems 80 or 90 is also significantly reduced, because there is no longer a need to cool the non-condensable dilution gas. This cost saving is amplified because the cost of cooling increases significantly as the intended cooling temperature decreases. The cost of cooling the dilution gases to the very low temperature of the second condenser is more than ten times than that of cooling the first condenser. Therefore, by removing the non-condensable gas from entering the second condenser, significant cooling cost reduction can be achieved.

In some embodiments, recovering system 80 may be implemented, when the one or more sterilization systems are relatively small, e.g., the chamber size is less than 150 liters, whereas recovering; system 90 may be implemented when the one or more sterilization systems are relatively large, e.g., chamber size may be greater or equal to 150 liters, in other embodiments, other chamber sizes may be considered small or large.

FIG. 10 is a flowchart depicting a method 1000 for recovering a sterilization agent from a waste gaseous mixture from one or more sterilization chambers, in accordance with some embodiments of the present disclosure.

Method 1000 may include receiving 1010 a waste gas from one or more sterilization chambers. The waste gas may include a gaseous mixture of a sterilization agent, nitrogen gas, and water vapor.

Method 1000 may include washing 1015 the gaseous mixture with water by a gas separator, thereby absorbing the sterilization agent and water vapor in the water, creating a water-gaseous sterilization agent mixture.

Method 1000 may include collecting 1020 the water-gaseous sterilization agent mixture at a bottom section of the gas separator and exhausting the nitrogen gas at a top section of the gas separator.

Method 1000 may include reducing 1025 a pressure of the water-gaseous sterilization agent mixture to a first predefined pressure so as to reduce a boiling point temperature of the sterilization agent to below a freezing point temperature of water in the water-gaseous sterilization agent mixture.

Method 1000 may include heating 1030 the water gaseous sterilization agent mixture to a temperature above boiling point temperature of the sterilization agent and above a freezing point temperature of the water to produce gaseous sterilization agent and water vapor.

Method 1000 may include cooling 1035 the gaseous sterilization agent and water vapor with the pressure at the first predefined pressure by a first condenser to a temperature below a boiling point temperature and above the freezing point temperature of the water vapor, and removing condensed water vapor from the gaseous sterilization agent.

Method 1000 may include raising 1040 the pressure of the gaseous sterilization agent by a separation pump, to a second predefined pressure greater than the first predefined pressure so as to elevate a boiling point temperature of the sterilization agent said separation pump being coupled to the first condenser, or the upper portion of the first tank.

Method 1000 may include cooling 1045 the gaseous sterilization agent at the second predefined pressure, by a second condenser, to a temperature below the boiling point temperature and above a freezing point temperature of the sterilization agent causing the sterilization agent to condense into a liquid.

Method 1000 may include collecting 1050 the liquid sterilization agent for reuse.

It should be understood with respect to any flowchart referenced herein that the division of the illustrated method into discrete operations represented by blocks of the flowchart has been selected for convenience and clarity only. Alternative division of the illustrated method into discrete operations is possible with equivalent results. Such alternative division of the illustrated method into discrete operations should be understood as representing other embodiments of the illustrated method.

Similarly, it should be understood that, unless indicated otherwise, the illustrated order of execution of the operations represented by blocks of any flowchart referenced herein has been selected for convenience and clarity only. Operations of the illustrated method may be executed in an alternative order, or concurrently, with equivalent results. Such reordering of operations of the illustrated method should be understood as representing other embodiments of the illustrated method.

Different embodiments are disclosed herein. Features of certain embodiments may be combined with features of other embodiments; thus certain embodiments may be combinations of features of multiple embodiments. The foregoing description of the embodiments of the disclosure has been presented for the purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure to the precise form disclosed. It should be appreciated by persons skilled in the art that many modifications, variations, substitutions, changes, and equivalents are possible in light of the above teaching. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the disclosure.

While certain features of the disclosure have been illustrated and described herein, many modifications, substitutions, changes, and equivalents will now occur to those of ordinary skill in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the disclosure. 

The invention claimed is:
 1. A system for recovering a sterilization agent from a waste gaseous mixture, the system comprising: a gas separator configured to wash waste gas from one or more sterilization chambers, with water, the waste gas comprising a gaseous mixture of a sterilization agent, inert dilution gases, and water vapor, thereby absorbing the sterilization agent and the water vapor by the water creating a water-gaseous sterilization agent mixture that is collected at a bottom section of the gas separator, and exhausting the inert dilution gases at a top section of the gas separator; a pressure reducing valve for reducing a pressure of the water-gaseous sterilization agent mixture to a first predefined pressure; a first tank or a gas evaporator, coupled to the pressure reducing valve, configured to receive the water-gaseous sterilization agent mixture, and to heat the water-gaseous sterilization agent mixture to a temperature above a boiling point temperature of the sterilization agent and above a freezing point temperature of the water to produce a gaseous sterilization agent and water vapor; a first condenser configured to receive the gaseous sterilization agent and the water vapor via the first tank or the gas evaporator, and to cool the gaseous sterilization agent and the water vapor to a temperature below a boiling point temperature and above a freezing point temperature of the water vapor at the first predefined pressure to produce condensed water vapor and to separate the gaseous sterilization agent from the condensed water vapor; a water tank, coupled to the first condenser, configured to receive the condensed water vapor, wherein when the first tank heats the water-gaseous sterilization agent mixture, the water tank is the same tank as the first tank, and when the gas evaporator heats the water-gaseous sterilization agent mixture, the water tank is in addition to the first tank; a separation pump coupled to the first condenser for raising the pressure of the gaseous sterilization agent to a second predefined pressure; a second condenser, configured to receive the gaseous sterilization agent from the separation pump, to cool the gaseous sterilization agent to a temperature below a boiling point temperature and above a freezing point temperature of the sterilization agent at the second predefined pressure causing the sterilization agent to condense into a liquid; and a second tank, coupled to the second condenser, for storing the liquid sterilization agent.
 2. The system according to claim 1, wherein the sterilization agent comprises ethylene oxide (ETO).
 3. The system according to claim 2, wherein the first predefined pressure is 1 pound per square inch and the second predefined pressure is atmospheric pressure.
 4. The system according to claim 3, wherein the boiling point temperature of water is 20 deg C. when the pressure of the gaseous mixture is 1 psi.
 5. The system according to claim 3, wherein the boiling point temperature of the ETO is 10 deg C. when the pressure of the gaseous mixture is atmospheric pressure.
 6. The system according to claim 1, wherein the sterilization agent is propylene oxide.
 7. The system according to claim 1, further comprising a chamber evacuation pump coupled to the gas separator for pumping the waste gas into the gas separator.
 8. The system according to claim 1, further comprising an exhaust warmer and a freezer economizer for recovering cooling energy in the system.
 9. The system according to claim 1, further comprising one or more H₂O freezers coupled to the first condenser and the separation pinup, and wherein each of the one or more H₂O freezers freezes H₂O molecules in the water vapor to a freezer surface.
 10. The system according to claim 9, wherein at least two H₂O freezers from the one or more H₂O freezers are connected in parallel, coupled between the first condenser and the separation pump.
 11. The system according to claim 1, further comprising one or more ETO freezers coupled to the second condenser for trapping residual vapors of the sterilization agent.
 12. The system according to claim 11, wherein at least two ETO freezers from the one or more ETO freezers are connected in parallel.
 13. The system according to claim 1, further comprising one or more ETO pre-condensers placed in series before the second condenser, wherein each of the one or more pre-condensers have progressively lower temperatures above the temperature of the second condenser.
 14. A method for recovering a sterilization agent from a waste gaseous mixture, the method comprising: receiving a waste gas from one or more sterilization chambers, the waste gas comprising a gaseous mixture of a sterilization agent, inert dilution gases, and water vapor; washing the gaseous mixture with water by a gas separator, thereby absorbing the sterilization agent and the water vapor in the water, creating a water-gaseous sterilization agent mixture; collecting the water-gaseous sterilization agent mixture at a bottom section of the gas separator, and exhausting the inert dilution gases at a top section of the gas separator; reducing a pressure of the water-gaseous sterilization agent mixture to a first predefined pressure so as to reduce a boiling point temperature of the sterilization agent to below a freezing point temperature of the water in the water-gaseous sterilization agent mixture; heating the water-gaseous sterilization agent mixture in a first tank to a temperature above the boiling point temperature of the sterilization agent and above a freezing point temperature of the water to produce gaseous sterilization agent and water vapor; cooling the gaseous sterilization agent and the water vapor with the pressure at the first predefined pressure by a first condenser, to a temperature below a boiling point temperature and above the freezing point temperature of the water vapor, and removing condensed water vapor from the gaseous sterilization agent; raising the pressure of the gaseous sterilization agent by a separation pump, to a second predefined pressure greater than the first predefined pressure so as to elevate a boiling point temperature of the sterilization agent, said separation pump being coupled to the first condenser, or an upper portion of the first tank; and cooling the gaseous sterilization agent at the second predefined pressure, by a second condenser, to a temperature below the boiling point temperature and above a freezing point temperature of the sterilization agent causing the sterilization agent to condense into a liquid, thereby collecting the liquid sterilization agent for reuse.
 15. The method according to claim 14, wherein the sterilization agent comprises ethylene oxide (ETO).
 16. The method according to claim 15, wherein the first predefined pressure is 1 pound per square inch (psi) and the second predefined pressure is atmospheric pressure.
 17. The method according to claim 16, wherein the boiling point temperature of water is 20 deg C. when the pressure of the gaseous mixture is 1 psi.
 18. The method according to claim 16, wherein the boiling point temperature of the ETO is 10 deg C. when the pressure of the gaseous mixture is atmospheric pressure.
 19. The method according to claim 14, wherein the sterilization agent is propylene oxide.
 20. The method according to claim 14, wherein exhausting the inert dilution gases comprises discharging nitrogen gas or CO) gas or a combination thereof, to the atmosphere or collecting the exhausted inert dilution gases comprising nitrogen gas or CO₂ gas or a combination thereof, for reuse.
 21. The method according to claim 14, further comprising recovering cooling energy in the system by using an exhaust warmer and a freezer economizer.
 22. The method according to claim 14, further comprising freezing H₂O molecules in the water vapor to a freezer surface of one or more H₂O freezers.
 23. The method according to claim 22, wherein at least two H₂O freezers from the one or more H₂O freezers are connected in parallel, and further comprising defrosting at least one of the H₂O freezers from the at least two parallel H₂O freezers.
 24. The method according to claim 14, further comprising trapping residual vapors of the sterilization agent using one or more ETO freezers coupled to the second condenser.
 25. The method according to claim 24, wherein at least two ETO freezers from the one or more ETO freezers are connected in parallel, and further comprising defrosting at least one of the ETO freezers from the at least two parallel ETO freezers.
 26. The method according to claim 14, further comprising setting the temperatures of each of one or more ETO pre-condensers placed in series before the second condenser to progressively lower temperatures above the temperature of the second condenser. 